I too have some severe frame drops in locations where it doesn't make any sense.
I'm running 4790K, 16 GB RAM and a 980ti. I get 60 FPS almost everywhere except for a few odd places.
Repcon facility is one of these. Camp McCarren interior hits my performance really hard.
The worst frame drops however are in the New Vegas sewers. Can drop from 60 to 20 for no discernible reason.
Pretty disgusting considering the rig I have. These areas drastically need optimisation.